X-ray detectors which have a gadolinium oxysulfide ceramic (UFC ceramic) as detector material are frequently used in computer tomography (CT). With the aid of this material, X-rays can be converted into visible light. The X-ray image is reconstructed from the electrical signal which is then formed using a linked photodiode.
When constructing these detectors, the detector material is structured by sawing in order in this way to obtain individual, small detector segments which are arranged next to one another and are separated from one another by the sawn grooves. A detector module of this type comprising a plurality of detector segments is linked to a photodiode module, which comprises a photodiode array, with photodiodes arranged next to one another in a suitable manner for the individual detector segments, and a conductor structure for reading the individual photodiode elements. A detector segment together with the associated photodiode element then forms an individual detector channel. The outer surfaces of the detector module which do not face the photodiode module are encased in an optically reflecting layer.
Likewise, the sawn grooves are separated using optically reflecting separating layers, generally referred to as “septa”. This ensures that the light which is generated in a detector channel by the impingement of X-ray quanta can be recorded sensitively and individually with the aid of the associated photodiode without radiation losses to the outside or into other channels occurring.
Hitherto, one-dimensionally structured linear detectors have been produced in the manner described. Whereas the outer reflector generally consists of a TiO2-filled epoxy resin (e.g. Araldite 2020®), the reflecting septa of detectors of this type are usually formed from an aluminum foil coated with TiO2-filled polymethyl methacrylate (PMMA). For other structuring operations, BaSO4-filled Hostaphan® sheets are also used for outer reflectors and as septum material.
However, faster CT appliances require detectors which are structured not just in one dimension but rather in two spatial directions, since these detectors allow the direct imaging of anatomical volumes. Hitherto, linear detectors have often been combined to produce a two-dimensional detector structure in matrix form.
For more economical production of new two-dimensionally structured detectors, it would be considerably more favorable for the two-dimensional structure to be produced in the detector material by suitable cross-sawing. However, unlike with one-dimensionally structured detectors, in the case of two-dimensionally structured detectors, it is very difficult if not impossible for the individual detector channels to be optically separated by the introduction of a sheet into the two-dimensional structure. It would therefore be advantageous for the septa to be produced by filling the structuring with a highly reflecting, castable, hardening reflector material.
A suitable moldable, curing material which is as far as possible light-proof and highly reflecting, has not however hitherto been available. The outer reflector material that has been used hitherto and includes a TiO2-filled epoxy resin is not optimally suitable for use as septum material, since the reflectivity is insufficient for a clean separation of the individual detectors. The reflectivity also cannot be improved by further increasing the TiO2 content, since the intrinsic reflection of TiO2 does not increase any further at a filling level above 20-25%. At the same time, higher filling levels, on account of the increase in viscosity of the uncured suspension, have an adverse effect on the penetration into narrow sawn gaps.